# Optical push broom effect by a moving refractive index front in a silicon Bragg waveguide

## TL;DR

Researchers demonstrated a new optical effect where a refractive index front captures and compresses a continuous wave signal in a silicon waveguide.

## Contribution

First experimental demonstration of the optical push broom effect in a silicon Bragg waveguide.

## Key findings

- A refractive index front captures and accelerates a CW signal near the Bragg grating band gap.
- A 2 ps free carrier front collects a 30 ps long signal packet.
- The effect enables temporal and spatial signal compression.

## Abstract

Here we report the first experimental demonstration of signal trapping by a refractive index front in a silicon waveguide with a periodic perturbation, the so-called optical push broom effect. The refractive index front generated by a fast pump pulse captures and confines the energy of a CW signal propagating with smaller group velocity near to the band gap of a Bragg grating introduced in the waveguide. The energy of the CW signal is shifted in frequency, accelerated to the front velocity and thus accumulated inside the front. In the experiment a 2 ps free carrier front was generated via two photon absorption of the pump in the silicon waveguide. It collects approximately a 30 ps long packet of the CW signal inside it. The presented effect can be utilized to compress signals in time and space.

The online version contains supplementary material available at 10.1038/s41598-026-36302-x.